Nonaqueous electrolyte secondary batteries such as lithium-ion secondary batteries have a high energy density as compared to other secondary batteries such as lead-acid batteries and alkaline secondary batteries, and are therefore widely used as power sources of portable devices such as mobile phones. In recent years, research and development directed to use of a nonaqueous electrolyte secondary battery as a power source of a mobile body such as an electric car is being actively conducted.
While nonaqueous electrolyte secondary batteries such as lithium-ion secondary batteries have a high energy density, they suffer from a degradation in battery performance such as a decrease in discharge capacity and an increase in internal resistance due to repetition of charge-discharge and long-term storage. Such a degradation in battery performance results mainly from a reaction between an electrode plate and a nonaqueous electrolyte, and attempts are made to add various additives to the nonaqueous electrolyte for suppressing a degradation in battery performance. For example, Patent Document 1 describes a compound having a S—O bond as an additive to a nonaqueous electrolyte.